With increasing interest in health in recent years, particular importance has come to be given to the blood fluidity as a health barometer. The blood fluidity is commonly called the degree of smoothness of blood flow, which signifies that a smooth blood flow with high fluidity indicates good health. One of the ways of checking the blood fluidity disclosed so far is a technique for measuring the time required for blood to run through a filter having a microscopically small groove (see Patent Literature 1 for example).
Incidentally, the blood of lower fluidity tends to be subjected to aggregation where blood cell is retained to be combined into conglomerates. The methods for evaluating such a phenomenon include a technique by which the number and area of the retained white blood cell are calculated from the blood flow image where only the white blood cells have been selected by separation (see Patent Literature 2) and a technique by which the aggregation rate of the red blood cell is calculated from the blood flow image where only the red blood cells have been selected by separation (see Patent Literature 3).
In the techniques described in the above-mentioned Patent Literatures 2 and 3, the blood is separated into only the white blood cell or red blood cell. Instead of such method of separating into specific blood cells, another proposed method determines the type of the blood cells from the blood flow image according to the brightness ratio and the dispersion thereof, whereby the number of the blood cells is calculated (see Patent Literatures 4 and 5).